An example of a band adjustment method of a polyphase filter is shown in FIG. 7 on the page 810 of “European solid-state circuits (IEEE EUROPEAN SOLID STATES CIRCUITS, 2002)”. This example is used in order to accurately adjust to 90 degrees a phase difference between output IQ signals, which are output differential signals from a Voltage Controlled Oscillator (VCO) converted by a polyphase filter. Note that patent document 1 discloses a configuration to input an output signal from a VCO into a polyphase filter.
FIG. 16 is a view illustrating a circuit configuration which is an example of a band adjustment device of a polyphase filter. The band adjustment device of the polyphase filter shown in FIG. 16 is composed of a VCO 5001, a polyphase filter 5002, a mixer 5003, a phase comparator 5004, and a phase-to-controlled voltage converter 5005. In such a configuration, firstly an output signal 5010 from the VCO is converted from a differential signal to an IQ signal 5011 by the polyphase filter. Next, this IQ signal is input to an LO port of the mixer and also to the phase comparator, and a phase error from 90 degrees is detected. Then, an output signal 5012 from this phase comparator is converted into a controlled voltage by the phase-to-controlled voltage converter, and a band of the polyphase filter is adjusted so as to reduce the phase error by the controlled voltage. At this time, the number of stages of the polyphase filter is one. By repeating the loop operation by this polyphase filter, the phase comparator, and the phase-to-control voltage converter for several times, the IQ signal with a small phase error is generated.
[Patent Document 1]
Japanese Unexamined Patent Application Publication No. 2006-339700